Performic acid (or peroxyformic acid) is considered an industrially important percarboxylic acid. Performic acid has an advantageous degree and range of microbiocidal properties compared to other peroxycarboxylic acids, such as peracetic and perproprionic acids, as disclosed by V. Merka et al in J. Hyg. Epidem. Microbiol. Immunol, 1965 (IX) 220, as well as in European Patent Application No. 863,098,96.
Peroxycarboxylic acid compositions are generally made through an acid catalyzed equilibrium reaction. Most often, the peroxycarboxylic acids are generated in a chemical plant, and then shipped to customers for on-site use. Due to the limited storage stability of peroxycarboxylic acids, the peroxycarboxylic acids must be packed in special containers and shipped under strict Department of Transportation (DOT) guidelines. Further, excess amounts of reagents (e.g., acids, oxidizing agents, and stabilizers) are present in the compositions during shipping to prevent decomposition. For peroxyformic acid, however, the inherent instability of the substance relative to the higher alkyl peracid, and the explosive nature of the substance at the concentrate make it an even more significant challenge to be manufactured, stored and transported before dilution prior to use, in the similar way like higher alkyl peracid. Thus, there are needs for the on-site generation of peroxycarboxylic acids, especially peroxyformic acid.
Performic acid is formed by part of the original reagents and reaction products form an equilibrium mixture. However, such a mixture may be rather unstable and/or reactive in handling and in storage, typically having a relative short shelf life. The stability of performic acid, in comparison to other peroxycarboxylic acids such as peracetic acid, presents stability challenges from 1-2 orders greater. For example, the half-life of performic acid is in the order of minutes to hours, compared to the half-life of peracetic acid which is weeks to months. Due to the characteristics of performic acid in having significantly lower shelf life stability there remains a need to provide in situ generation for use on-site without requiring storage and/or shipment.
Performic acid is extremely useful and effective in various field of technology such as disinfection, in spite of its instability. Formed from the reaction of hydrogen peroxide and formic acid, it reacts more rapidly and powerfully than peracetic acid before breaking down to water and carbon dioxide. Performic acid is an environmentally friendly oxidizing biocide for various disinfection applications. The application areas involve microbial growth control and cleaning of surfaces in larger industrial scale such as municipal or industrial waste water purification, or for circulation of process waters in pulp and paper industry. These compositions are most applicable for example in hospitals, dental surgeries, kitchens, and bathrooms to kill infectious organisms.
Performic acid solutions are highly reactive. If performic acid solutions are contacted with impurities such as zinc dust, lead dioxide, or sodium azide they may react violently and decompose. Performic acid typically decomposes as such into carbon dioxide and water within a few hours at ambient temperature and pressure.
Typically, performic acid is formed by reacting aqueous formic acid with aqueous hydrogen peroxide through an exothermic reaction in the present of a strong mineral acid catalyst, such as sulfuric acid. Due to its instability, performic acid solutions should be prepared in situ preferably at the point of use or directly before use depending on the properties of the reactants and reaction points. However, the presence of strong mineral acid, such as sulfuric acid, in pipes can lead to corrosion of the material and contamination of the process stream.
Accordingly, it is an objective of the invention to provide a method for generating performic acid in situ without the presence of an acid catalyst, such as a strong mineral acid catalyst.
A further objective of the invention includes providing a method for generating performic acid in situ employing with heat as the only catalyst, without additional chelating and/or stabilizing agents.
A still further objective of the invention is to provide on-site generator apparatus for a continuous flow reaction with variable rates of generating performic acid.
Additional objectives of the invention include generating the performic acid as well as mixed peracid compositions including performic acid in situ. Other objects, advantages and features of the present invention will become apparent from the following specification taken in conjunction with the accompanying drawings.